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Little Blair Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Blair Valley clear sky chart from 2005-11-05 to 2020-06-03.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
64%
19905
40%
57879
28%
19861
75%
19861
61%
25213

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
64%
897
35%
2912
30%
896
74%
896
48%
1341
January16th to endNight
61%
960
42%
2910
31%
960
75%
960
50%
1372
February1st to 15thNight
61%
880
40%
2645
30%
877
76%
877
53%
1197
February16th to endNight
50%
792
39%
2375
28%
792
67%
792
46%
1125
March1st to 15thNight
50%
900
36%
2674
25%
900
68%
900
51%
1212
March16th to endNight
51%
960
39%
2595
21%
960
68%
960
57%
1197
April1st to 15thNight
41%
899
40%
2249
14%
899
58%
899
53%
1109
April16th to endNight
46%
892
45%
2230
14%
892
64%
892
67%
995
May1st to 15thNight
51%
692
44%
2042
21%
692
65%
692
70%
784
May16th to endNight
45%
706
44%
2117
19%
705
62%
705
67%
795
June1st to 15thNight
56%
637
40%
1911
25%
637
66%
637
78%
709
June16th to endNight
66%
630
37%
1890
26%
630
72%
630
81%
703
July1st to 15thNight
82%
600
34%
1800
26%
600
85%
600
70%
745
July16th to endNight
80%
691
35%
1910
25%
656
82%
656
63%
861
August1st to 15thNight
85%
825
39%
2060
23%
821
87%
821
78%
941
August16th to endNight
89%
892
43%
2230
29%
892
91%
892
76%
1035
September1st to 15thNight
84%
840
42%
2210
30%
840
89%
840
77%
973
September16th to endNight
76%
836
48%
2310
36%
836
86%
836
80%
923
October1st to 15thNight
64%
840
47%
2310
30%
840
80%
840
69%
989
October16th to endNight
74%
896
48%
2669
40%
896
86%
896
75%
1034
November1st to 15thNight
74%
880
41%
2860
37%
880
84%
880
65%
1117
November16th to endNight
68%
900
40%
2925
36%
900
78%
900
54%
1248
December1st to 15thNight
63%
900
37%
2925
33%
900
71%
900
47%
1359
December16th to endNight
59%
960
37%
3120
30%
960
71%
960
46%
1449

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
111212346%73%
58522
Night
111212235%75%
58084
TransparencyDay
11%3412%26%40%
58220
Night
10%2413%27%40%
57887
SeeingDay
314%28%32%17%3
9540
Night
19%21%32%26%7%
19914

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
3213313347%65%
2016
16th to endDay
221232345%7%63%
2366
February1st to 15thDay
3112213347%67%
2201
16th to endDay
21341446%8%61%
1979
March1st to 15thDay
2112213448%67%
2276
16th to endDay
111222435%6%68%
2681
April1st to 15thDay
1112323346%70%
2689
16th to endDay
11245%80%
2665
May1st to 15thDay
1112136%79%
2897
16th to endDay
1122485%
3053
June1st to 15thDay
111125%84%
2758
16th to endDay
1111387%
2730
July1st to 15thDay
1112212436%70%
2730
16th to endDay
121232346%8%63%
2849
August1st to 15thDay
11221334475%
2473
16th to endDay
11121235%6%72%
2676
September1st to 15thDay
111212335%75%
2408
16th to endDay
1111112284%
2310
October1st to 15thDay
111223480%
2310
16th to endDay
111232481%
2256
November1st to 15thDay
11113345%75%
1989
16th to endDay
112223446%69%
2025
December1st to 15thDay
332325%45%7%61%
2025
16th to endDay
321232345%8%63%
2160
January1st to 15thNight
1212323347%65%
2912
16th to endNight
3212213346%67%
2910
February1st to 15thNight
22223337%70%
2641
16th to endNight
123335%5%7%65%
2375
March1st to 15thNight
2211213348%67%
2674
16th to endNight
11121245%8%69%
2595
April1st to 15thNight
112212335%74%
2249
16th to endNight
1123483%
2230
May1st to 15thNight
11226%82%
2042
16th to endNight
1112388%
2116
June1st to 15thNight
1111289%
1911
16th to endNight
1111289%
1890
July1st to 15thNight
1111345%77%
1890
16th to endNight
1211212246%72%
2020
August1st to 15thNight
11223481%
2070
16th to endNight
1111123382%
2230
September1st to 15thNight
111223382%
2210
16th to endNight
111290%
2310
October1st to 15thNight
111123482%
2310
16th to endNight
1111235%82%
2669
November1st to 15thNight
11113335%78%
2860
16th to endNight
1112222245%71%
2925
December1st to 15thNight
2213314447%63%
2925
16th to endNight
32232335%7%64%
3120

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
18%45%15%28%26%
2017
16th to endDay
17%47%17%28%24%
2366
February1st to 15thDay
15%35%14%29%30%
2201
16th to endDay
16%5%7%18%28%22%
1979
March1st to 15thDay
14%3419%31%26%
2276
16th to endDay
14%45%16%33%25%
2681
April1st to 15thDay
12%35%14%37%25%
2689
16th to endDay
6%2314%34%38%
2665
May1st to 15thDay
8%2312%30%43%
2897
16th to endDay
41311%34%43%
3056
June1st to 15thDay
5%118%22%60%
2758
16th to endDay
5%11311%76%
2730
July1st to 15thDay
14%349%16%50%
2591
16th to endDay
16%5%8%17%25%27%
2696
August1st to 15thDay
13%338%24%47%
2459
16th to endDay
12%349%23%46%
2676
September1st to 15thDay
12%348%20%51%
2408
16th to endDay
6%12425%58%
2310
October1st to 15thDay
9%229%27%48%
2310
16th to endDay
7%247%23%54%
2256
November1st to 15thDay
9%3412%28%40%
1989
16th to endDay
12%45%15%26%34%
2025
December1st to 15thDay
19%5%5%20%23%26%
2025
16th to endDay
18%5%6%21%28%18%
2160
January1st to 15thNight
17%46%17%28%27%
2912
16th to endNight
16%45%18%24%30%
2910
February1st to 15thNight
13%4414%28%33%
2652
16th to endNight
15%5%7%16%29%25%
2375
March1st to 15thNight
14%36%18%30%26%
2674
16th to endNight
10%36%15%33%28%
2595
April1st to 15thNight
12%25%15%36%26%
2249
16th to endNight
6%1312%33%43%
2230
May1st to 15thNight
5%1313%29%46%
2043
16th to endNight
4119%36%45%
2117
June1st to 15thNight
47%23%62%
1911
16th to endNight
5%138%80%
1890
July1st to 15thNight
9%246%19%58%
1800
16th to endNight
13%27%16%26%34%
1910
August1st to 15thNight
7%2310%24%51%
2060
16th to endNight
8%228%24%54%
2230
September1st to 15thNight
7%237%22%56%
2210
16th to endNight
5%1328%60%
2310
October1st to 15thNight
7%2210%28%48%
2310
16th to endNight
6%149%22%56%
2669
November1st to 15thNight
9%2310%32%41%
2860
16th to endNight
14%2414%30%33%
2925
December1st to 15thNight
17%46%18%26%26%
2925
16th to endNight
17%5%7%20%26%22%
3120

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
8%16%20%34%16%3
225
16th to endDay
417%26%34%15%2
446
February1st to 15thDay
419%28%33%11%2
446
16th to endDay
5%31%30%24%8%
398
March1st to 15thDay
5%25%35%23%8%1
450
16th to endDay
425%35%23%10%1
480
April1st to 15thDay
5%23%36%21%10%1
449
16th to endDay
223%34%23%12%2
438
May1st to 15thDay
219%34%28%11%3
468
16th to endDay
123%34%25%13%2
522
June1st to 15thDay
113%31%29%19%4
444
16th to endDay
1333%29%25%6%
435
July1st to 15thDay
1222%38%28%7%
425
16th to endDay
317%37%30%10%
455
August1st to 15thDay
1221%39%27%7%
419
16th to endDay
117%42%28%9%
460
September1st to 15thDay
1330%41%17%5%
435
16th to endDay
111%26%40%17%2
435
October1st to 15thDay
114%34%37%11%
435
16th to endDay
110%26%33%25%4
360
November1st to 15thDay
19%20%44%20%3
225
16th to endDay
120%21%30%20%5%
225
December1st to 15thDay
411%20%40%23%1
225
16th to endDay
5%18%22%29%19%4
240
January1st to 15thNight
29%17%34%26%9%
900
16th to endNight
49%19%33%26%6%
960
February1st to 15thNight
111%20%31%25%9%
884
16th to endNight
218%27%29%17%5%
792
March1st to 15thNight
316%26%29%20%3
900
16th to endNight
117%27%27%19%5%
960
April1st to 15thNight
222%32%23%16%4
899
16th to endNight
119%32%24%17%5%
892
May1st to 15thNight
15%32%32%16%2
693
16th to endNight
119%33%29%13%2
707
June1st to 15thNight
7%34%35%20%2
637
16th to endNight
1229%40%23%3
630
July1st to 15thNight
1112%44%34%5%
600
16th to endNight
211%46%36%4
691
August1st to 15thNight
110%40%37%9%
825
16th to endNight
25%33%46%11%
892
September1st to 15thNight
111%34%43%8%
840
16th to endNight
15%15%32%35%10%
836
October1st to 15thNight
19%23%33%24%6%
840
16th to endNight
5%17%30%30%15%
896
November1st to 15thNight
5%17%38%28%9%
880
16th to endNight
28%17%27%29%14%
900
December1st to 15thNight
38%18%35%26%8%
900
16th to endNight
410%21%30%25%7%
960
Page generated at 2020-06-04 00:18:52. Version ac04

Copyright 2020 A. Danko


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